This invention relates to an optical recording material and a process therefor, and more particularly to an optical recording material having a first recording layer obtained by imagewise exposing a photosensitive material and a second recording layer or a reflective thin film layer, and a process therefor.
Heretofore, a magnetic material has been mainly used as a recording material embedded in cards such as a credit card and a bank card. In the case of this magnetic material, recording and readout of information can be readily carried out. However, the alternation of information is readily carried out, and it is impossible to carry out high density recording.
In order to solve such problems, there has been proposed an optical recording material wherein a photosensitive material is imagewise exposed to form light transmissive portions and light screening portions to write information in the photosensitive material, and this information is read out by the difference of optical transmittancy. When such an optical recording material is embedded in a card substrate to use it as a recording material for a card, there are the following problems.
(a) In many cases, various printing compositions are applied to the surface of the card substrate, and therefore preferably the card substrate is opaque. However, in order to imbed the optical recording material as described above, it is necessary that the substrate exhibits at least partial light transmission properties. This is significantly disadvantageous from the standpoint of the production of the card.
(b) In the case of the recording material as described above, it is difficult to sufficiently increase the difference in light transmission properties at the light transmissive portions and the light screening portions. Further, when the written information is intended to be read by the difference in transmittancy, soil on the surface of the card greatly affects readout.
Accordingly, an attempt has been made to to read out information by the difference in optical reflectivity rather than transmittancy. For example, there have been proposed cards having a recording layer wherein silver particles are dispersed in a gelatin matrix. Writing of information in the recording layer is carried out by irradiating the recording layer with a laser beam to form recording pits. The recording layer can be continuously produced by a coating process, and uniform reflectivity can be obtained over a wide region of wavelength by using silver. Furthermore, it is possible to apply to a record playback apparatus wherein a laser beam having various wavelengths is used. However, when recording is carried out by a photographic process, it is difficult to simultaneously improve optical reflection and definition. For example, when the development time is increased, optical reflection is improved, but recording portions (exposed portions) tend to increase and definition may be lowered. On the contrary, when the development time is shortened, definition is improved, but light reflection may become poor. When readout is carried out, a contrast between recorded portions and non-recorded portions is not clear.
Further, there has also been provided a so-called heat mode recording material wherein a recording layer of recording material is irradiated with an energy beam such as a laser beam in the form of spots to change the state of part of the recorded layer thereby recording. Thin films of metals such as tellurium and bismuth, thin films of organic compounds such as polystyrene and nitrocellulose, films of tellurium low oxides (phase transition) or the like are used as the recording layer for use in the heat mode recording material. These recording materials do not require development treatment after writing of information, and are so-called DRAW (direct read after write) media. It is possible to carry out high density recording, and it is also possible to carry out an additional writing. Accordingly, it was expected that use of this type of recording materials for discs or cards can be increased.
Among these heat mode recording materials, the most widely used recording material is one wherein a thin film of metals such as tellurium and bismuth is vapor deposited of a substrate. In this recording material, writing of information is carried out by irradiating the metallic thin film with an energy beam such as a laser beam in the form of spots to remove the metal of irradiated portions by vaporization or fusing, thereby to form pits. Readout of information is carried out by irradiating the recording layer with a readout light and reading out the difference in reflectivity between the pit portions which are recording portions and metallic thin film which are non-recording portions. In writing information, in addition to the formation of the recording pits which correspond to information per se to be read out, it is necessary to write in the recording layer a tracking which corresponds to a guide groove for light as well as preformatting for specifying the pits to be read out.
However, metals such as tellurium and bismuth from which the recording layer is produced have toxicity to some extent, and therefore full care must be taken in handling. Further, the formation of pits by irradiation of an energy beam such as a laser beam requires high control technology. Furthermore, the pit formation steps are complicated and therefore the cost is not always low. Accordingly, if there is developed a recording material wherein a tracking corresponding to a guide groove for light as well as preformatting for specifying pits to be read out can be inexpensively formed in a large scale by simple processes other than laser beam irradiation, it is expected that such a recording material will have extremely high usefulness.
On the other hand, there have been proposed cards having a recording layer wherein silver particles are dispersed in a gelatin matrix. Writing of information in this recording layer is carried out by irradiating the recording layer with a laser beam to form pits. The recording layer can be continuously produced by a coating process, and the use of silver affords uniform reflectivity over broad wavelength regions. Further it is possible a apply to record/playback apparatus wherein a laser beam having various wavelength regions is used. However, such a recording layer is made of silver, and therefore the cost is high. Further, it is difficult to stably and inexpensively produce and supply due to fluctuation of the price of silver. Furthermore, the pattern formation and development treatment must be carried out in a dark place in certain cases.